Arrangement in a wheel lifting mechanism

ABSTRACT

The present invention relates to an arrangement in a wheel lifting mechanism designed to lift at least one wheel ( 1 ) running on an underlying surface so that it is capable of negotiating an obstacle (h) rising above the underlying surface. The arrangement comprises an element ( 7 ) which is formed with a contour convexly curved towards the underlying surface and is moveably supported in relation to the axle of the wheel ( 1 ). The said element is designed, when the contour of the element ( 7 ) engages with the obstacle (h), to bring about the said lifting of the wheel ( 7 ) as the element ( 7 ) is rotated about its point of engagement with the obstacle (h). The arrangement further comprises a chassis ( 4 ), to which the wheel axle is firmly connected. Between the chassis and the element ( 7 ) there is an operative connection designed, when the element ( 7 ) engages with the obstacle (h), to allow the chassis ( 4 ) firstly to undertake lifting of the wheel ( 1 ) from a home position of the element ( 7 ) during a displacing movement relative thereto in the direction of movement of the wheel, and secondly to bring about a return to the home position once the wheel ( 1 ) has been lifted to the level of the obstacle (h).

The present invention relates to an arrangement according to thepre-characterising part of claim 1.

In many contexts small rollers or wheels are used on trolleys, machineframes, Zimmer frames etc. Small wheels or rollers take up little space,are relatively strong and not least can help to keep costs low.So-called pivot wheels to facilitate steering and turning are alsoknown.

One prerequisite for the use of the aforementioned small rollers orwheels, however, is that the underlying surface is flat. Door thresholdsand kerb edges constitute obstacles that are difficult to surmount.Since the pushing force is often applied high up, there is a risk of thewheeled arrangement overturning. Even though the wheels used on Zimmerframes, for example, are relatively large, their capacity to roll upkerb edges, for example, is poor. The person using the Zimmer frame thenhas to manage to tilt it backwards far enough to allow its front wheelsto mount the kerb edge. It is not as awkward for the trailing wheels,since the natural movement in pushing the Zimmer frame forwards alsolifts these wheels up. In order to get the front wheels up, however, thehandle of the Zimmer frame has to be drawn backwards and downwards,which is an unnatural movement for a person using the Zimmer frame assupport. Not only Zimmer frames have this problem, but also cleaningtrolleys, wheel chairs, serving trolleys and shopping trolleys etc.

U.S. Pat. No. 3,239,872, DE 4040283 A and JP 10297206 A, for example,already disclose wheel lifting mechanisms of the aforementioned type,which are all fairly similar to one another in that the element used tobring about the wheel lifting is only rotatably mounted. This means thatthe mechanism requires a relatively large overall height and despitethis requires a relatively large pushing force in order to negotiate araised obstacle.

The object of the present invention is to provide an improved wheellifting mechanism and this is achieved in that the mechanism has thecharacteristic features specified in the characterising part of claim 1.

Further advantages and characteristics of the invention are set forth inthe dependent claims and the following description of a preferredexample of an embodiment, which is illustrated in the drawing attached.In this drawing FIG. 1 shows a side view of a wheel lifting mechanismaccording to the invention, and with three different positions of alift-producing element, FIG. 2 a–2 f show a side view of the wheellifting mechanism in various positions when negotiating an obstacle,FIG. 3 shows the wheel lifting mechanism in FIG. 1, FIG. 4 indiagrammatic form shows how various inclinations are obtained innegotiating obstacles of different height, and FIG. 5 shows the movingprinciple of the wheel lifting mechanism in FIG. 1.

The wheel lifting arrangement shown in the drawing interacts with pivotwheels comprising two wheels or rollers 1 arranged on a common axle 3,which is fixed to a chassis 4. Also forming part of the chassis is acasing 2, which at a front end accommodates a bearing housing 5 having ashaft 6 projecting vertically upwards, which is in turn fixed to theobject that is to be moved, such as the front, largely vertical legs ofa Zimmer frame, for example. An inclined element 7 is displaceablysupported in relation to the chassis 4. From its elevated end theunderside 13 of the element 7 initially slopes down steeply and thenmore shallowly towards a bottom point directly above the point ofcontact of the wheel 1 with the underlying surface. The element 7 isfurthermore displaceably mounted, which is achieved by means of a frontroller 8 supported in elements and a rear roller 9 supported in thechassis 4. The roller 8 is designed to roll on a race 10 on theunderside of the chassis 4 and the roller 9 on a race 11 on the innerupper side of the element. On its downward-facing surface the element 7is provided with a friction-enhancing coating 12, of rubber for example,which may also be ribbed. A spring 13 is furthermore fixed to thechassis 4 and is designed by means of split castors 14, 15 and a cord 16in the element 7 to tension this towards its upward and forward homeposition. The fact that the spring 13, throughout the entire movement ofthe element 7, is anchored to the element 7 situated between the rollers8, 9 means that the element 7 will be held fast by the spring 13 withthe rollers 8, 9 in contact with the respective races 10, 11. Moreover,a relatively short spring movement is obtained despite a long workingstroke between the element 7 and the chassis 4.

FIG. 1 shows three different relative positions between the chassis 4and the element 7. In order to show these more clearly the variouspositions of the roller 8 have been marked 8, 8′ and 8″ respectively.These positions correspond to the positions shown in FIGS. 2 a, 2 c and2 d respectively, as will be explained below.

FIG. 2 a illustrates how the element 7 of the wheel lifting mechanismaccording to the invention, which is in its home position in relation tothe chassis 4, encounters an obstacle h and in so doing comes to a halt.The chassis 4 and the unit such as a Zimmer frame carried by the chassiscontinue in the direction of movement (to the right in the figure).FIGS. 2 b–2 d show different stages during the lifting sequence. In FIG.2 e the wheel 1 once more has contact with the obstacle h, which meansthat the element 7, through a displacing movement in relation to thechassis 4, returns to its home position, that is to say the positionshown in FIG. 2 a.

When the wheel lifting mechanism according to the invention encountersan edge, the coating 12 of the element 7 comes first into contact withthe edge. Under a continuing forward movement of the wheel liftingmechanism, the chassis 4 slides forwards (in relation to the element 7)whilst the chassis 4 and hence also the wheels are lifted upwards by theinteraction between the rollers 8, 9 and the races 10, 11. Ultimately,the chassis 4 has moved to such an extent that the wheels 1 come intocontact with the edge and begin to roll thereon. As a result the element7 is released and the spring 13 is drawn forwards into its home position(see FIGS. 2 a–2 e).

It can be seen from FIG. 4 how obstacles of various heights come intocontact with the element 7. Its downward-facing edge or surface, that isto say the one that comes into contact with the obstacle, has a shapesuch that (in the home or rest position) it has a slight inclinationclosest to the wheel, which then becomes ever steeper as it progressesupwards and forwards. Even low obstacles therefore strike the elementrelatively far forward. The steering of the element relative to thechassis can well be described as partially a displacing movement by theroller 8, which is supported in the element 7, along the race 10 andpartially a rotational movement around the roller 8. The rotationresults from the fact that roller 9 continuously bears on the race 11throughout the displacing movement. This description of the movementaffords the opportunity to describe how all points on the element 7 movein relation to the chassis 4. Of particular interest are the pointswhich come into contact with obstacles, for in the wheel lifting thispoint remains stationary, which means that the movement of the element 7relative to the chassis 4 at this point also describes the movement ofthe chassis 4 over the obstacle. Lower obstacles, which encounter theelement 7 lower down, give a larger radius for the rotational movement,which means that its vertical component increases as the obstaclediminishes and is subtracted from the vertical component of thedisplacing movement. This means that low obstacles also impart a longdisplacing movement to the chassis 4 before the wheel takes over. Inother words, a lower rise and thereby a comfortable negotiation of theobstacle is achieved for obstacles of low to medium height, which maythereby become virtually imperceptible.

Instead of using two wheels each situated either side of the element 7,it is also feasible to arrange one element on either side of a centrallyarranged wheel, which also affords the advantage that the two elementscan more readily manoeuvre the wheel lifting mechanism for negotiating akerb edge at right angles, for example. Furthermore it is possible toarrange the leading edge of the element a fraction in front of theswivel axis of the wheel lifting mechanism, since when the wheel losesits contact with the ground the arrangement will be immediatelyswivelled towards a position at right angles. This can also be achievedby a single central element, provided that this is sufficiently wide.

According to an alternative embodiment (not shown), there is only onewheel 1 and one element 7, these being arranged in tandem withcoincident centre lines.

The arrangement according to the invention can also be used, aftercertain design modifications, to cushion the descent from a kerb edge byallowing the rear end of the element to jut out somewhat behind thewheel. When the wheel then rolls over the edge, the element catches theedge and gives a softer lowering of the wheel.

The element 7 can, like the entire wheel lifting mechanism, be composedof pressed sheet metal parts, die cast aluminium or injection mouldedplastic, and the rollers 8, 9 bearing against the races 10, 11 may beball bearings, roller bearings or slide bearings.

It may be noted that the two races may but do not necessarily have to becircular races. The element may furthermore be positively guided in someother way, even one involving the use of two springs.

The design of the two races offers great freedom of choice in so far asthe obstacle-clearing movement is concerned, as is exemplified by FIG.5. In FIG. 5 the race 11 is curved and the lower roller 9 supported inthe wheel arrangement rests against the inside of the race 11. At theupper end of the element 7 the roller 8 supported therein is in contactwith the race 10 in the chassis 4. This race, as will be seen from thisembodiment, is slightly S-shaped, with the result that when coming upagainst an obstacle, the incipient lifting movement is slight, beforethen progressively increasing to a maximum value and then diminishingagain in proximity to the rear end position. In this case the movementwhen negotiating an obstacle will be initiated and concluded very gentlyand almost imperceptibly.

A straight movement over an obstacle is achieved if the race 10 isslightly convex towards the element 7. The simplest from a purely designstandpoint is naturally a normal curve 10, but this presupposes that theapplication will allow the movement to become steeper the more thevehicle inclines in negotiating the obstacle.

By arranging the downward-facing surface 12 of the element 7 and therace 11 on the inside thereof so that they are not altogether parallel,the free movement of the wheel, that is to say the height through whichthe wheel lifts the vehicle over obstacles, which is determined by wherethe element delivers the obstacle over to the wheel, can be varied fordifferent obstacle heights.

1. Arrangement in a wheel lifting mechanism designed to lift at leastone wheel (1) running on an underlying surface so that it is capable ofnegotiating an obstacle (h) rising above the underlying surface, thearrangement comprising an element (7) which is formed with a contourconvexly curved towards the underlying surface and is moveably supportedin relation to the axle of the wheel (1), and which is designed, whenthe contour of the element (7) engages with the obstacle (h), to bringabout the said lifting of the wheel (1) as the element (7) is rotatedabout its point of engagement with the obstacle (h), wherein thearrangement comprises a chassis (4), to which the wheel axle is firmlyconnected, and that between the chassis and the element (7) there is anoperative connection designed, when the element (7) engages with theobstacle (h), to allow the chassis (4) firstly to undertake lifting ofthe wheel (1) from a home position of the element (7) during adisplacing movement relative thereto in the direction of movement of thewheel (1), and secondly to bring about a return to the home positiononce the wheel (1) has been lifted to the level of the obstacle (h) andthat the operative connection between the element (7) and the chassis(4) comprises a first race (11) remote from the upper side of theelement (7) and having a profile corresponding to the contour, and asecond race (10) facing the first race (11) and connected to the chassis(4), a first member (8) fixed to the element (7) and designed in thehome position to bear against the front part of the second race (10) andto be moved backwards along this during the lifting, a second member (9)fixed to the chassis (4) and designed in the home position to bearagainst the rear part of the first race (11) and to be moved forwardsalong this during the lifting, and a sprung third member (13), actingbetween the element (7) and the chassis (4) and designed to bring abouta return to the home position after the lifting.
 2. Arrangementaccording to claim 1, wherein the said first and second member (8, 9) isa slide bearing.
 3. Arrangement according to claim 1, wherein the saidfirst and second member (8, 9) is a bearing.
 4. Arrangement according toclaim 1, wherein the said third, sprung member (13) is a helical coilspring.
 5. Arrangement according to claim 1, wherein the convexly curvedsurface of the element facing the underlying surface is provided with afriction-enhancing coating (12), for example one of ridged rubber. 6.Arrangement according to claim 1, wherein a wheel (1) is provided onboth sides of the element (7).
 7. Arrangement according to claim 1,wherein the second race (10) is curved in an S-shape.